Previously, OSHA had an 8-hour TWA limit of 0.1 ppm for chlorine dioxide. The ACGIH recommends the same time-weighted average and a 15-minute STEL of 0.3 ppm. The proposal retained the same TWA and added a 15-minute STEL of 0.3 ppm, and NIOSH (Ex. 8-47, Table N1) concurred with these limits, which are established in the final rule. Chlorine dioxide is a red-yellow gas at ordinary temperatures.
Rats exposed to 0.1-ppm concentrations of chlorine dioxide for 10 weeks at five hours daily showed no adverse effects from exposures. Other data in animals are not available (Dalhamn 1957/Ex. 1-307).
Data on human exposures indicate that marked irritation occurs on inhalation of 5 ppm (no time specified), and that one death occurred at 19 ppm (Elkins 1959b, as cited in ACGIH 1986/Ex. 1-3, p. 118). Repeated exposures in humans have been linked to bronchitis and pronounced emphysema (Petry 1954/Ex. 1-1163). Clinical studies conducted by Gloemme and Lundgren (1957/Ex. 1-323) revealed that the majority of workers who had been exposed for five years to average concentrations of chlorine dioxide below 0.1 ppm, in combination with about 1.0 ppm chlorine, experienced eye and respiratory irritation and slight bronchitis. Some gastrointestinal irritation was also observed in these workers. Gloemme and Lundgren (1957/Ex. 1-323) attributed all of these effects to elevated short-term exposures involving excursions above the 0.1 ppm level. Ferris, Burgess, and Worcester (1967/Ex. 1-316) have shown that concentrations occasionally ranging as high as 0.25 ppm were associated with respiratory effects in workers concomitantly exposed to chlorine. The United Paperworkers International Union (UPIU) supported the development of comprehensive standards for irritant gases such as chlorine dioxide.
In the final rule, OSHA is retaining the 0.1-ppm 8-hour TWA and adding a 15-minute STEL of 0.3 ppm for chlorine dioxide. The Agency concludes that both of these limits are necessary to protect workers against the significant risk of respiratory, skin, and eye irritation known to occur as a result of short-term exposures above the TWA of 0.1 ppm. OSHA has determined that these adverse effects constitute material impairments of health.